Investigation of the Influence of the Local Microstructure of Copper Interconnects on Void Formation and Evolution during Electromigration Testing

Abstract

The electromigration‐induced void evolution has been investigated in‐situ on fully embedded inlaid copper test structures inside a SEM, utilizing the method described in [1]. After the failure of the test structure or after significant voiding had been observed the cathode via region of the samples was prepared for subsequent TEM and/or EBSD analysis in order to reveal the position of grain boundaries and the orientations of the grains in the neighborhood of a void. It was confirmed that intersections of grain boundaries with interfaces of the interconnect lines or clusters of small grains can act as nucleation sites for initial void formation or as trapping sites on which voids can be stopped. Furthermore, it was found that for interconnects with strengthened top interface, where the diffusion rate is significantly lower due to the changed chemical bonding, that the void movement occurs mainly along the copper/liner interface. Such interconnects show significantly longer lifetimes. In this paper, local a...